One of the leading contributors to air pollution is the internal combustion engine which is used to power all types of motor vehicles, be they cars, trucks or motorcycles. Exhaust from the engines in these vehicles contains various pollutants, such as carbon monoxides, nitrous oxides, unburned hydrocarbons, aldahydes and particulate contaminants.
The Federal Government requires that all vehicles sold and registered for use on the highways must meet specific standards as to the amount of pollutants emitted in the vehicle exhaust. Many states, including California, have initiated mandatory inspection and maintenance procedures during which the pollutants in the vehicle exhaust are monitored and compared with predetermined standards. If the vehicle emissions fail to meet these standards, the vehicle must be repaired so the emission standards are met. In California, the process is referred to as a "smog check," and various service stations or smog check stations are authorized to check the vehicle emissions to see if they meet the state imposed requirements.
State and Federal new vehicle emission standards and control requirements are stated in "grams per mile." Several test procedures have been developed to indicate the pollutants in the exhaust gas, and to extrapolate the "grams per mile" from the test procedures. One such method is the constant volume sample test (CVS test) which is included in the Federal Test Procedure that is required for new vehicle certification. This test measures vehicle exhaust emissions under simulated dynamic conditions such as a vehicle would normally experience. The results of this procedure are the measurement of vehicle mass emissions in terms of grams per vehicle mile travelled. In order to accomplish this measurement, the entire exhaust stream emitted from the vehicle is captured via the "CVS" system, and a representative sample is collected for analysis. During this test, the vehicle is operated on a dynamometer to simulate the vehicle traveling a predetermined distance. Knowledge of this distance, and specific exhaust volume produced, with measurement of a proportional sample of exhaust gas concentrations, enables a quantitative calculation of emissions to be expressed as "grams per mile." The CVS test is an exacting, time consuming, and expensive process costing up to one thousand dollars per test, making the test unsuitable for use in more than a limited number of tests on a limited number of vehicles.
Inspection and maintenance programs for monitoring and controlling vehicle emissions on existing vehicles have employed emission testing processes which are less costly than the CVS test. These processes, however, are far less accurate since they do not even attempt to measure vehicle mass emissions under the dynamic conditions which the vehicle typically experiences. Several processes have been suggested or used. The one process in greater use is the "idle" test procedure, which monitors vehicle emissions at idle speeds while the vehicle is stopped. These idle tests typically determine the concentration of various constituents of the exhaust gas, in parts per million (PPM). These tests do not attempt to correlate the exhaust gasses to the actual mass emissions of the vehicle, as in a grams per mile measurement. The PPM measurement has been found to relate to vehicle equipment malfunctions and is thus useful in determining the gross emission characteristics, and to predict failure of vehicle equipment affecting the vehicle exhaust emissions.
The idle emission standards are typically set at limits sufficiently high to accommodate equipment errors, operator errors, and calibration errors. Since idle emissions only "relate" to actual operating emissions, high limits must be set in order to avoid incorrectly failing vehicles. The result of this process is that many vehicles with faulty or substandard emission equipment, escape the test and maintenance requirements and continue to operate with high emissions which pollute the environment.
A short form dynamic measurement process, sometimes called a "loaded mode test" has been proposed as a more accurate testing technique for verifying vehicle emissions in the field for inspection and measurement purposes. This test is performed on a dynamometer, and measures exhaust emission concentrations at idle speeds, and also at higher speeds and vehicle loads. Although more efficient in determining component failures, there is no accurate measurement of the actual mass emissions in the vehicle exhaust. Further, while superior to the "idle test," many vehicles would still escape necessary maintenance and pollute the environment. A further drawback, is the high cost of the testing equipment, such as chassis dynamometers, and exhaust analyzers, which require a high monetary investment for each test station. Further, the loaded mode tests require a larger amount of time to conduct for each vehicle (up to 20-30 minutes). Since there are some 12 million vehicles in California alone, a smog test system is needed that can process several cars per minute, not just a few cars per hour.
Currently in California, the smog check is performed by hooking up a test analyzer system to the exhaust pipe of a vehicle in order to measure the pollutants. This test process samples the exhaust emissions only at idle speeds and is therefore less comprehensive than a dynamic test condition. The smog check can be performed at any of a large number of authorized service stations or smog check stations, but still requires a considerable amount of time and results in inconvenience for the vehicle owner, especially since most smog check stations make you leave the vehicle so the smog check can be performed at the convenience of the station operator, rather than at the convenience of the vehicle owner. Tampering studies have shown that smog check requirements are being circumvented by disconnecting the smog control equipment on the vehicle except when needed for the smog check.
There is thus needed a device which can analyze the pollutants in a vehicle exhaust quickly and cheaply, without causing the vehicle owner to wait an extended period of time, and which further produces results which are more accurate and more tamper-proof.
Most smog checks also have a further disadvantage in that the engine is not being run in a loaded mode when the smog check is taking place. The largest percentage of pollutants are produced during the acceleration of a vehicle rather and maintaining a constant velocity under load, than in stationary idle. Thus, if the smog check is run with vehicles stationary, the transmission not engaged, and no load exerted on the engine, the smog check does not accurately measure the engine pollutants during normal vehicle operation. A device is thus needed to measure the exhaust pollutants during a realistic operation period of the vehicle.